One type of touch sensor device operates by way of capacitance sensing utilizing capacitance sensors. The capacitance detected by a capacitance sensor changes as a function of the proximity of a conductive object to the sensor. The conductive object can be, for example, a stylus or a user's finger. In a touch sensor device, a change in capacitance detected by each sensor in the X and Y dimensions of the sensor array due to the proximity or movement of a conductive object can be measured by a variety of methods. Regardless of the method, usually an electrical signal representative of the capacitance detected by each capacitive sensor is processed by a processing device, which in turn produces electrical or optical signals representative of the position of the conductive object in relation to the touch sensor pad or touch sensor screen in the X and Y dimensions. A touch sensor strip, slider, or button operates on the same capacitance-sensing principle.
One type of touch sensor device is composed of a matrix of rows and columns. Within each row or column, there are multiple sensor elements. However, all sensor pads within each row or column are coupled together and operate as one long sensor element. The number of touches a touchpad can detect is not the same as the resolution of the touchpad. For example, even though a touchpad may have the capability to detect two substantially simultaneous touches with an XY matrix, such touchpads cannot resolve the location of the two substantially simultaneous touches. One way to resolve the location of a second touch is if the touches arrive sequentially in time. This allows the remaining three potential locations to be evaluated to determine which locations are “actual touch” locations and which are invalid touches, also referred to as “ghost touch” locations. If both touches arrive or are detected substantially simultaneously, there is no way to resolve which of the two pairs of potential locations constitute “actual” touches, instead of invalid touches (e.g., “ghost” touches). Thus, such two-axis touchpads are configured to resolve only a location of a single touch. Similarly, current touch screens are designed to detect the presence and location of a single touch.
Touch pads that detect multiple touches may use a counting technology which iterates through the sensors, examining the signals caused by the detected capacitance. When a non-zero data value following a zero (inactive sensor) is encountered, it marks that sensor as the start of a conductive object. The system continues iterating and increments the size of the conductive object until another inactive sensor is found, indicating the end of the conductive object. An inactive sensor must be present between conductive objects in order to detect two touches. However, if two fingers are placed close together on the slider, they will appear as only one touch, since there are no inactive sensors between the fingers.